Patent GB-1305076-A (GB)
IPC: C22C1/02
Filed: 1970-09-11
Abstract: 1305076 Automatic control of alloy concentration in steel making GENERAL ELECTRIC CO 11 Sept 1970 [15 Sept 1969] 43467/70 Heading C7D [Also in Division G3] During the "finishing step" in a steel-making process the composition of molten metal 11b Fig. 1 in a vat 10 of an electric arc furnace, is analyzed by a spectrographic analyzer 21 and a control system 17 (more detailed in Fig. 2) controls the addition of alloy ingredients to the melt, sequentially and proportionately by weight, in order to achieve a desired concentration of each alloy ingredient within the end product metal alloy. The control system also takes into account the melt temperature as sensed by a thermocouple 22; and the dissolved oxygen content of the molten bath sensed by an analyzer 100 and adds an alloy ingredient and alloy material to the bath to bring the oxygen content to a desired value. In the control system Fig. 2, signals significant of the desired final composition of the bath are produced by a unit 120 in dependence on the grade of steel selected by an operator. Thus the unit 120 produces a dissolved oxygen set point O 2 - SP , a temperature set point T SP  and the composition set point COMP  SP , which set points are fedto summing junctions 121, 122, 123 respectively. The summer 121 produces an output corresponding to the difference between the set point and an actual dissolved oxygen content signal (O 2 )  SCAN  produced by a calculator 124 from values derived by the analyzer 100 Fig. 1. The summer 122 produces an output significant of the difference between the set point temp. signal and the actual bath temp. signal derived by thermocouple 22. The summer 123 performs parallel summations, the set point signal COMP SP , representing the desired concentration levels of a plurality of elements for example - aluminium, calcium, silicon, zirconium, ferro-silicon, and manganese. These desired levels are compared with actual concentration levels of the respective ingredients derived by the spectrograph analyzer 21 Fig. 1 and the summer 123 produces a plurality of output signals rep-  resenting deviations of actual levels from desired levels, and hence the required change in concentration level of each alloy element. Each summing junction may be a digital computer. The output signals of the summing junctions are fed to a "process model" 124 which responds to the signals to produce alloy material addition set points AL1 SP , AL2 SP  ... ALn SP . These set point values are selectively coupled by a switch unit 137 to a weight controller and are combined with signals from respective sensors 111-114 which measure the alloy material weight transferred from the respective storage bins 102-105 to a conveyer 115 and thence via a chute 116 to the vat. Controller 138 may be analogue or digital. If additional alloys are to be added to the melt or bath, the process model 124 senses when the output of the weight controller goes to zero and advances the switch unit 137 to the next set point and so on until all the alloys specified by the process model are added. Fig. 5 (not shown) sets forth the steps of  another embodiment of the process control system 17 and which are particularly suitable for implementation by means of a digital computer.